In a coil of conductive wire, such as a solenoid, the thinly insulated wire of the coil must be terminated at each end and joined to a source of electric power. Usually, this is accomplished by connecting each end of the coil wire to a connector which in turn connects to a larger heavily insulated power wire. Many methods exist for making the coil wire connection. Screw clamps, crimps, wire-wrapped pins, spring-loaded IDCs (Insulation Displacement Connectors), soldered joints, and welded joints, are among the most common.
When the coil wire is thick and robust, all of the above methods are satisfactory. But, when the coil wire is thin and fragile it must be handled gently and until now, soldering has been accepted as a practical low-cost industrial method for coil wires less than 35 AWG (American Wire Gauge). However, soldering presents various problems.
Since July of 2006, products sold and used within the European Community have to comply with the Regulation of Hazardous Substances (RoHS) directive, which is legislation which aims to keep hazardous materials from being dumped into the environment. The element lead (Pb) is among the materials banned by this legislation.
Lead (Pb) has been used in tin/lead solder for many years and performs a stabilizing and melting-temperature-control function. The RoHS ban brought about a rush for compliance, in which “lead-free” alternative solders were developed for the electronic industry, where the use of solder is entrenched. Much study and debate continues addressing the economics and the reliability of the alternatives.
Those industries outside of the electronics industry have historically not been as wedded to the use of solder. However, where connections to coil wire below 35 AWG are sought, there has not historically been any alternative to the use of solder. In these other industries, the RoHS directive prompted lobbying for exemptions from the environmental directives banning the use of lead in solder.
Exemptions have been provided by the RoHS in recognition of the extreme difficulty of compliance with the new regulations with regard to certain applications of lead (Pb). One such exemption is where a solder must withstand a higher temperature than the melting point of the commonly used tin/lead solder or its lead-free alternatives. In these cases, high melting point solders with high lead (Pb) content are still allowed.
It is believed that the pursuit of exemptions may have been manipulated by reclassifying applications as “high temperature applications” to enable the lead-based solder to be used for high-melting-point solder. Paradoxically, this process may lead to more lead (Pb) being used than was the case prior to the imposition of the new rules. However, it is anticipated that the above-mentioned loopholes will be closed and secondly that the exemptions will in any case have a limited time span. It is anticipated that, eventually, lead-based solder will be completely banned.
Moreover, the RoHS directive is not the only impediment to using solder. Soldering is a dangerous and unpleasant task. The possibility of nasty burns is ever present and the fumes given off by the heated acid flux are unpleasant and unhealthy. Additionally, the intense study of solder that RoHS promoted exposed many failure modes, not fully recognized and understood before. Among these were such serious flaws as internal voids, age cracking, conductor corrosion, and an inconsistency of application. Perhaps the most frightening aspect is that these flaws are only discoverable by destructive examination or by x-ray. Even if the examination finds no flaws, doubt of reliability remains because of the inconsistency of soldering.
The cost and difficulty of pursuing exemptions from RoHS compliance and of the use of lead-free solder may be avoided by establishing connections with thin fragile coil wire without using solder. However, the solder-free methods of the prior art severely distorted, notched, squeezed and scraped the coil wire in order to break through the insulation and make a good connection. The use of this approach, which employs relatively high forces, incurs a limit when applied to fragile wires. This limit is defined by the point (force level) at which breakage of the wire occurs, which breakage renders the wire useless, and which therefore incurs considerably expense. Accordingly, there is a need in the art for an improved system and method for establishing conductive connections with wire, such as coil wire, without using solder, and without damaging the wire.